Servomechanism



Dec. 20, 1960 H. c, ZEISLOFT 2, 7

SERVOMECHANISM Filed Dec. 51, 1959 2 Sheets-Sheet 1 IN VEN TOR.

Dec. 20, 1960 H. c. ZIEISLOFT 2,965,076

- SERVOMECHANISM Filed Dec. 51. 1959 2 Sheets-Sheet 2 IN VEN T OR.

United States Patent SERVOMECHANISM Harry C. Zeisloft, Brookfield, Wis.,assignor to General Motors Corporation, Detroit, Mich, a corporation ofDelaware Filed Dec. 31, 1959, Ser. No. 863,291

Claims. (Cl. 121-147) My invention relates to fluid-operatedservomechanisms, and is particularly directed to new and improved meansfor controlling such mechanisms. The invention is particularly suited tomechanisms operated by air or other gases, but is also applicable tohydraulic servomotors.

There are many servomechanisms or power actuators which depend forcontrol upon varying the pressure in a chamber or the relative pressuresin two chambers. Some of these achieve this pressure variation bymodulating an air jet. The jet may be allowed to flow freely from anozzle to a port from which it is discharged to the mechanism to beactuated; or the flow may be partially or completely intercepted ordiverted to reduce the pressure recovered in the discharge port.

My invention involves a mode of control for this purpose which, so faras I am aware, has not been known previously, and which has substantialadvantages that will be apparent from the succeeding detaileddescription of preferred embodiments of the invention.

To summarize it, the control according to my invention embodies acontinuously moving shutter-like mechanism which rapidly andintermittently obstructs the flow from the nozzle to the discharge port.The fraction of the period of rotation of the shutter during which theflow is obstructed may be varied by a suitable input control. Theaverage pressure recovered in the discharge port is varied by varyingthe phasing of the shutter, or, in other words, varying the part of theperiod of rotation during which the shutter obstructs the flow.

The principal objects of the invention are to provide an improvedservomechanism, and particularly a servomechanism which is highlyresponsive and accurate in its response.

The presently preferred embodiments of my invention are illustrated inthe accompanying drawings, in which Figure l is a somewhat schematicsectional drawing of one form of the invention in which the shutter iscontrolled mechanically.

Figure 2 is a fragmentary sectional view of the same taken on the planeindicated by the line 2-2 in Figure 1.

Figure 3 is a partial schematic view of a second form of the inventionembodying electrical mechanism for varying the shutter opening.

Referring first to Figure 1, there is illustrated an ap paratus in whicha control device according to the invention actuates a relay or pilotvalve which, in turn, controls the flow of actuating fluid to a powercylinder. The operating fluid will be referred to hereinafter as air inthe interest of conciseness, although the invention is not limited toair as a motive fluid. The relay or pilot valve identified asltl'comprises a housing 11 bored to provide a cylinder 12, one end ofwhich is closed by a plug 13. A valve spool 14 freely reciprocable inthe cylinder has relatively broad lands 17 at each end thereof andknife-edge leads 18 at the central portion of the valve spool. Air'under pressure is supplied from any suitable source through an inletport 19 into a chamber 21, which connects with the cylinder 12 betweenthe lands 18 in the neutral or centered position of the valve spoolillustrated. The housing 11 also defines two passages 22 whichcommunicate with the cylinder 12 between the lands 17 and 18 at each endof the spool. Suitable piping 23 or other means defining a conduit forthe servo fluid connects the chambers 22 to the opposite ends of a'power cylinder 25. Cylinder 25 houses a reciprocable piston 26 whichsupplies power to the device to be actuated through a piston rod 27. Oneend of the cylinder is closed by a removable head 29. The structure ofthe servomotor or power cylinder 25 and the piping to it are notdescribed in detail, since they may be of any suitable structure and thedetails are immaterial to the invention. Air under pressure may besupplied to either end of cylinder 25 from port 19 through chamber 21and a passage 22 upon displacement of valve spool 14 from 'a neutralposition. Such displacement also uncovers one or the other of two ventports 30* by which the air is discharged to atmosphere from the otherend of the cylinder.

Movement of the spool 14 to control the servo cylinder 25 is efiected bya mechanism according to the invention which comprises a continuouslyrotating shutter 32 consisting of two sector disks 33 and 34 closelyadjacent each other and rotating about a common axis. Disk 33 isintegral with or fixed to a shaft 35, the lower end of which issupported in a bearing 37 in the housing 11. Disk 34 is integral with orfixed to a'hollow shaft 38 coaxial with shaft 35. Shaft 38 is supportedin a suitable bushing in a casing 39 bolted to the upper surface ofhousing 11. Casing 39 and recesses in the upper surface of housing 11define a chamber 41 within which the shutter 32 rotates. A convergingnozzle '42 provided in the housing 11 discharged into the chamber 41.Nozzle 42 is supplied from the pressure fluid chamber 21, the fluidpassing around the valve spool 14. A funnel-shaped or convergingdischarge port 43 in the casing 39 is coaxial with the nozzle 42.Discharge port 43 communicates through passages 45 and 46 in the casing39 and housing 11 with a chamber 47 in one end of cylinder 12. It willbe noted that the common axis of nozzles 42 and discharge port 43 liewithin the radius of shutter 32. A passage '49 outside the periphery ofthe shutter connects the chamber 41 with a chamber 50 at the oppositeend of cylinder 12 from chamber 47.

The structure of shutter 32 will be more clearly apparent from Figure 2.Each sector disk 33 and 34 comprises a central disk 51 and twosector-shaped lobes 53 extending outwardly therefrom. The lobes 53 arepreferably about 78 degrees in arcuate extent. As shown in the drawings,the lobes on the two disks are partially overlapped so that the shutter32 obstructs flow from the nozzle to the port 43 through approximatelydegrees in each degrees of rotation. Thus, the two sets of lobesobstruct the flow during approximately of a cycle of rotation of theshutter. A greater period of obstruction can be had by increasing thephase difference of the disks 33 and 34; or, by decreasing the phasedifference, the relative period of obstruction may be decreased to aminimum of approximately 43% of the total period of revolution.

At some phase angle between the two disks, the relative obstruction toflow from nozzle 42 through discharge port 43 as compared to that fromnozzle 43 through outlet 49 will be such that the average pressures inthe chambers 47 and 50 will be equal. Decreasing the phase angle of thedisks from this point will increase pressure in chamber 47 and decreasepressure in chamber 50. Increasing the phase angle from this pointwillreduce the pressure in chamber 47 and increase it in chamber 50. It willbe understood that during that part ofthe cycle in which the flow isunobstructed between the nozzle and discharge port 43, the pressure inchamber 47 is higher than that in chamber 50 because of the pressurerecovery resulting from the direct flow from nozzle 42 into port 43 andbecause of the aspirating action of the flow which reduces the pressurein chambers 41 and 50. Because of the rapid or intermittent fluctuationsof pressure as the shutter rotates, valve spool 14 has a slight tendencyto oscillate or jitter, which greatly reduces static friction andhysteresis of the valve 14.

Proceeding now to the mechanism illustrated in Figure l for driving theshutter and varying the phase angle of the dis-ks, this mechanism ismounted in a case 54 which comprises a lower part 55 bolted to the uppersurface of housing 39 and an upper part 56 bolted to the lower part 55.The case 54 houses driving mechanism for the shafts 35 and 38 which ispowered by a small motor 57 mounted on a bracket 58 extending from thepart 56. Motor 57 may conveniently be an electric or air-driven motor.

The shaft of motor 57 is pinned to the hub 61 of a driving pinion 62.This hub is internally splined to receive the splined upper end 63 ofshaft 35, which is thus driven directly by motor 57. Pinion 62 drives apinion 65 integral with a shaft journalled in a fixed point in the part56. Pinion 65, in turn, meshes with an internally toothed ring gear 66,the hub of which is rotatable on shaft 35. Ring gear 66 has a second setof internal teeth which mesh with a planet pinion 67 rotatably mountedon a spider 69 journalled in the lower case part 55 so as to berotatable about the axis of shafts 35 and 38. The upper end of the outershaft 38 is journalled in the spider 69 and mounts a pinion 70 whichmeshes with pinion 67. An arm 71 integral with the spider 69 extendsthrough a slot in case 54. The outer end of arm 71 may have a hole 73 bywhich it may be connected to any suitable linkage or other device whichprovides the input to the servomechamsm.

Pinions 62 and 70 are of the same diameter and number of teeth, andlikewise pinions 65 and 67. Therefore, for anygiven fixed position ofspider 69, the shafts 35 and 38 are driven at the same speed by motor57. Movement of arm 71, through the planetary action between gear 66 andpinions 67 and 70, adds or subtracts to the movement of disk 34 by themotor and thereby changes the phase angle between the disks. Therefore,if arm 71 is moved in either direction from the position at which thepressures on valve spool 30 are balanced, the pressures in chamber 47and 50 will be unbalanced to move the valve spool in one direction orthe other, depending upon the direction of movement of the input 71.

It will be noted that the disposition of the vent ports 30 is such thatthey act to prevent excessive displacement of valve spool 14, since suchexcessive movement vents the chamber 47 or 50 which has the higherpressure and is tending to cause the valve overtravel.

Figure 3 is a fragmentary view illustrating another type of mechanismfor operating the shutter 32. The structure of the servomechanism,except as illustrated in Figure 3, may be the same as that alreadydescribed in connection with Figures 1 and 2. The shafts 35 and 38'correspond respectively to shafts 35 and 38 of Figure 1. In themechanism of Figure 3 each shaft is driven by a synchronous electricmotor, and the phase relation of the shutter disks is varied by varyingthe relative Phase of the operating currents of the motors. Asillustrated, shaft 35' is connected through bevel gears 75 and shaft 77to a two-phase motor 78. Shaft 38' is connected through bevel gears 79to the shaft 81 of a two-phase motor 82. The two motors are energizedfrom a mum mon two-phase A.C. supply 83. Motor 82 is directly connectedto the three wires 85, 86 and 87 of the two phase supply. Motor 78 isenergized through leads 89, and 91 by a phase shifting transformer 93energized from the leads 85, 8'6 and :87. The relative phase of thecurrent supplied to the two motors may be varied by the control handle94 of the phase shifter.

As will be apparent, the form of the device shown in Figure 3 could beenergized directly by the phase shift between two circuits whichindividually respond to two quantities which are to be brought into somedesired relation by the operation of the servomotor. For example, theservomotor could respond to the relative phase angles of two generatorsto control the supply of operating fluid to the prime mover of one ofthe generators for synchronizing purposes, in which case the motors 78and 82 could be connected to the two generators and the phase shifterwould not be required.

For the reasons outlined in the preceding paragraph, and also because ofits mechanical simplicity, the device of Figure 3 has some advantages.However, in other installations, the mechanical phase shifting device ofFigure 1 may be advantageous. One advantage of the servomotor of Figurel is that the motor 57 may be of any type. It may be an electric motorof any type or, if desired, it could be a small fluid motor suppliedfrom the same source that supplies motive fluid to the inlet port 19.

In general, it is apparent that many varieties of structure may beadopted to utilize the principle of intermittent obstruction of one ofthe ports leading to the device to be controlled, exemplified by theshutter mechanism illustrated in Figures 1 and 2. It will also beapparent that for some installations, where a high degree of force isnot required from the output device, a member corresponding to the valvespool 14 may be the output member of the servomotor rather than a relaymember which in turn controls a power cylinder such as 25. It is notessential for the shutter shafts such as 35 and 38 to be coaxial or evenparallel. It is only necessary that the sector disks be disposed so asto overlap between nozzle 42 and collector port 43.

The detailed description of preferred embodiments of the invention forthe purpose of explaining the principles thereof is not to be consideredas limiting the invention, since many modifications within the scope ofthe invention may be made by the exercise of skill in the art.

I claim:

1. A fluid-operated servomechanism comprising, in combination, meansdefining a chamber, a nozzle discharging into the chamber, meansdefining a pressure fluid inlet to the nozzle, means defining adischarge port from the chamber coaxial with the nozzle, means definingan outlet from the. chamber remote from the nozzle, a displaceablemember connected to the discharge port and the outlet port so as to bebiased in opposite directions by the pressures of fluid communicated tothe member through the said ports, and means for inversely modulatingthe said pressures comprising a continuously rotating variable shutterdisposed between the nozzle and the discharge port so as tointermittently pass and obstruct flow from the nozzle to the dischargeport, and means for varying the configuration of the shutter so as tovary inversely the relative duration of passage and obstruction of thesaid flow to the discharge port.

2. A fluid-operated servomechanism comprising, in combination, meansdefining a chamber, a nozzle discharging into the chamber, meansdefining a pressure fluid inlet to the nozzle, means defining adischarge port from the chamber coaxial with the nozzle, means definingan outlet from the chamber remote from the nozzle, a displaceable memberconnected to the discharge port and the outlet port so as to be biasedin opposite directions by the pressures of fluid communicated to themember through the said ports, and means for inversely modulating thesaid pressures comprising two continuously rotating sector disksdisposed between the nozzle and the discharge port so as tointermittently pass and obstruct flow from the nozzle to the dischargeport, and means for varying the relative phase angle of the disks so asto vary inversely the relative duration of passage and obstruction ofthe said flow to the discharge port.

3. A servomechanism as recited in claim 2 including a motor drivingcoupled to both sector disks and phase shifting mechanism connecting themotor to one of the sector disks.

4. A servomechanism as recited in claim 2 including two motors, onemotor being drivingly coupled to each sector disk, and means for varyingthe phase relation of the motors.

5. A fluid-operated servomechanism comprising, in combination, meansdefining a chamber, a nozzle discharging into the chamber, meansdefining a pressure fluid inlet to the nozzle, means defining adischarge port from the chamber coaxial with the nozzle, means definingan outlet from the chamber remote from the nozzle, a displaceable memberconnected to the discharge port and the outlet port so as to be biasedin opposite directions by the pressures of fluid communicated to thememaseaoao her through the said ports, and means for inverselymodulating the said pressures comprising a continuously rotatingvariable shutter disposed between the nozzle and the discharge port, soas to intermittently pass and obstruct flow from the nozzle to thedischarge port, means for varying the configuration of the shutter so asto vary inversely the relative duration of passage and obstruction ofthe said flow to the discharge port, and means responsive to apredetermined displacement of the displaceable member for venting thepressure applied to the said member tending to displace the said member.

References Cited in the file of this patent UNITED STATES PATENTS1,590,558 Stenhouse June 29, 1926 1,777,758 Mathieson Oct. 7, 19301,988,749 Reswick Jan. 22, 1935 2,079,041 Ryan et a1. May 4, 19372,198,543 Lauterbach Apr. 23, 1940 UNITED STATES PATENT OFFICECERTIFICATION OF CORRECTION Patent Nb, 2,965 O76 v December 20 1960Harry Cc Zeisloft It is hereby certifiedthat error appears in the abovenumbered patent requiring correction and that the said Letters Patentshould read as corrected below.

Column 5 line 4, for "driving" read drivingly =0 Signed and sealedthis27th'day of June 19610 (SEAL) I I Attest: v

ERNEST W. SWIDER I DAVID L. LADD Atte ting Officer I Commissioner ofPatents

